Automatic device for compensating magnetic speed-indicators for variations in temperature.



- E. M. THGMPSON. 'AUTOMAIIC DEVlCE FOR-COMPENSATING MAGNETIC SPEED INDICATORS FOR VARIATIONS IN TEMPERATURE. APPLICATION FILED MAY 21. I913.

Patented May 2,1916.

ham/v0 UNITED STATE.;BATE

EDW R .r ro yrrson, or BE IL i To tilltchlo'm "it Witty concern.

J i {it known that I, EDWARD M; THoM'r sojxj 'a citiz' enof'tlie'Unite'd States, residing l tLBeI it' iii thecounty of Rock, State of 'wisconsimliaye made anew and useful Invention in Automatic Devices for Compensating hla gnetic Speed-Indicators for Variations in Atmospheric Temperature, of which the. followingis a" specification.

.This invention relates to devices for antoniatically compensating magnetic Yspeed indicators, and similar instruments for va riations in atmospheric;temperature.g

" Theobject the invention is to provide means which are simple and-efficient forcorrecting the errors of indication of speed in dieatorsjantl similar dev ces of t-he m'agnetlc'type due to the etiects of-var ati'ons 11natmospherictemperatures... 7

Afurther. object of thefinvention is to. provide. means tori automaticallyvarying the condltlon ofthe magnetic field of magnetic speedometerslor(other siiiii'lar devices,

7 Referring to the accompanying thereto'o'f temperaturecompensating devices byan'd-in accordancewith variations irratmospheric temper'atur'e, whereby to secure pheric temperatures.

accurac or indication. at. dili'erent at'mos- 1 A; further ob ect of i. the invention is td -prov1de means of the nature and character referred to, and automatically moving the magnet or the 'fieldconcentrating mass or armature, the one relatively to and; from the other.:tox accomplish the compensation of 1i errorsof'indication due to variatiOns in atmospheric temperatures.- p

I Otherobj'ects of :theinventionwill appearmore fully hereinafteizi This invention consists substantially .in

the construction, combination, location and embodying the principles-of my invention. Fig. 2,, aj yiewfin'central longitud nal-section of ajtmagneticspeed indicator show ng the temperature compensating devices ap M FQMWEWA YMAG yamsmit T Specification of Iletterslaterit i.

u I consrn assrenon 9T0 @srEw rtrgwAnNnR eSBEEDOl/{EQEER comeotr -lama,. or. ELQIT. WISCONS1N ...'A,c aroaarnxon; o'rf vita-- ar e it a l Patented May 2.1916; 1913; seri inmi'oasi. i pliecl thereto in accordance with the prinip r my invention, the plane of sectlon being indicated by the line 2, 2, Fig. 1.

Fig.3, is a transverse sectional view on the line-3'. Fig. looking in the direction of the arrows. F igs t; 1s a broken detail view in section on the line i, 4:, Fig. l.

T'he same part is designated by the same,

reference numeral wherever throughouttheseveral views. I Thejes'sential elements of a magnetic speed indicator include meansfor producing a 1'0: tatmg magnetic 'field anda displaceable member normally but yieldingly biased or it occurs vand which member is subjected to the action ofsaid field whereby it is displaced from its initial position'to an extent which is proportional tdthespeed at which the means restrained in an initial or zero position,

for; producing the rotating magnetic field .is driyen. In one form of concrete embodiment of speed indicator including these elements. the rotating magnetic field' is'xproduced by rotating a permanent magnet from or inJpr-oportiona] relation to the part the speed of which is to be indicated by the instrument. The member which'is subjected to the influence of the resulting rotating magnetic field, and which is normally but yieldin'gly biased to an initial or zeroposition,- is in. the form of an electrically conductive member; the action of the rotating magnetic field producing therein electric currents which exert a drag effect uponsaid member tending to displace it from its initial or zero position to an extent depending upon the strength of the rotating magnetic field. Associated with the displaceable member is one element of a scale-andpointer device for indicating the extent'of displacement of the member.

In devices of this nature it has been the custom to so adjust the instrument that the indications' thereof will be correct at all speeds for. a given atmospheric temperature,say ordinary shop temperature. The electric conductivity of the displaceable member.however; varies with its temperature. As the temperature increases the resistance thereof increases, and any increase in such resistance decreases the magnetic drag exerted thereon by the rotating magnetic field. Similarly any decrease in temtrically conductive material, such, for in-' IIi8I 1i3 are lower while at the lower temperatures they are .rotating magnetic field. The result is that at higher atmospheric temperatures the speed indications or readings of the 'instru than the actual or true speed higher than actual or true speed. 1

It is among thespecial purposes of mypresent invention to provide means for making automatic correction of variations .or

errors in the readings of such instruments.

due to.variations in'atmospheric temperatures, and inthe accomplishment of these special purposes I employ a concentrating device, which in one form of -em odiment comprises a ring ofsoft iron'or other similar material arranged as an armature for the permanent magnet and so disposed relatively to the magnet as to concentrate the magnetic field of the latter within the space in which the displaceable member is positioned and, in accordance with the principle's of my invention, I provide 'means actuated by and in accordance with variations in atmospheric temperature to vary the effect of said magnetic field. upon the displaceable member. In a more restricted and limited sense, I propose to automatically shiftthe position of the armature, which, for convenience, may be called the magnetic mass, toward and from the magnet, and to accomplish such automatic shifting of the disk by and in accordance with variations inatmospheric temperatures.

In the drawing I have shown an opera tive practical embodiment of my invention, for the purpose of illustrating the principles thereof, and whereino, is a casing in which is mounted a permanent magnet 6, shown in this instance, as a magnet ofthe split ring type, and designed'tov be axially rotated through suitable connections (notshown) from the part .the speed of which is to be indicated. Mounted within the casing is a stationa'rily held cup 7 the top plate 8, and bottom 9, of which, carry bearings'in which is jqurnaled ashaft 10.

stance, as aluminum. Associated with this member is one element 'of a s'cale-and-pointer device. In this instance a circular flange 12 of the member 11, ca'rries a scale 13, which cooperates with a fixed pointer 1-1, the

latter being disclosedthrough a transparent field. Upon' this shaft I to rotate therewith is the member 11 ofelectial or zero position with reference to the pointer 14. The armature or magnetic mass pended from the itOP plate 8, of the cupT, I

by the bi-metallic strips 19. In the par ticular form shown threeof such strips are employed and these are disposed in symmetrical relation with respect to each other and the ring 18 which they support. Each strip 19 is composed of two short straight flat pieces of'metal having relatively different'coefiicients-of expansion under the effects of heat, and each is secured at one end'v to @a U post .20,'carried: by the ring 18, while at its other'end each strip has a threaded 'stud 21, screwed into it. The studs 21 work freely through openings in the top plate 8,.and are provided with heads 22, which'fit into c'ountersunk seats in the outer surface of plate 8. Each stud 21, carries a coil spring 23, which is interposed-between the plate 8 and the bar or strip 19. V

At the given or shop temperature at which the instrument is initially adjusted and calibrated, the bimetallic bars or strips 19, are preferably straight and flat,'but under the influence of variations from the given or shop "temperature these strips assume a curvature in greater or-less degree and in one direction or the other, according to the extent'of suchtemperature variation, and accordingto whether such variation is to a higher or a lower temperatute than that at which the 'instrumentis adjusted or calibrated. This action causes the magnetic mass 18 to be shifted toward or away from the magnet, as the case may be, thereby correspondingly varying the condition of the magnetic field, that is making it stronger in case of higher temperatures and weakening it in case of lower temperatures to compensate for the corresponding variations in the electrical resistance of the displaceable member,v and .the resulting variations in the drag action exerted thereon by the magnetic The arrangement above described results in a flexibility of connection of one end of each of the bimetallic bars which enables them'to properly accomplish their functions of shifting the field ring bodily toward and fromthe surface of the magnet without tilting said ring, and without binding or buckling the bars.

\Vhile'I have shown and described one specific form of device embodying the principles 'ofmy invention it is evident. that many specifically different structures-may be devised to carry out said principles. I do not d-r'sire, therefore, 1n the broadest scope of my invention, as defined 1n the clalms, to

be limited or restricted to the exact and specific structure shown and described.

What I claim as new and useful and of my own invention, and desire to secure by Letters Patent is p 1. In a magnetic speed indicator, a magnet mounted to rotate, a magnetic mass asend to said mass and loosely supported at its other end, and an electrically conductive scale member interposed between said magnet and mass.

3. In a magnetic speedindicator, a magnet mounted to rotate, a magneticmass arranged in juxtaposition to said magnet, posts carried by said mass, bimetallic strips each having one end secured to a post on the mass, means for loosely supporting the other .end of each strip, and an electrically conductive scale member interposed between'the mass and magnet.

4. In a magnetic speed indicator, a mag net mounted to rotate, a magnetic mass arranged in juxtaposition to said magnet. a

support for said mass including bimetallic strips each having one end attached to said mass, a stud carried byithe other end of each strip, a supporting member in which said studs are movably mounted and an electrically conductive scale member interposed between said mass and magnet. v p

5. In a magnetic speed indicator, a magnet mounted to rotate, a magnetic mass arranged in juxtaposition to said magnet, a support for said mass including bimetallic strips each having one end attached to said mass, a stud carried in the other end of each strip, a supporting member in which said studs are movably mounted, a spring interposed between said supporting member and each strip, and an electrically conductive scale member interposed between said magnet and mass. p

6. In a magnetic speed indicator, a magnet and a magnetic mass associated together, one of these parts mounted to rotate, bimetallic strips each connected atone end to said mass. means for loosely supporting the other end of each strip, and an electrically conductive scalemember interposed between said mass and magnet.

In testimony whereof I have hereunto set my hand in the presence of the subscribing witnesses, on this 23d day of May A. I). 

